The disposition currently used consists of connecting an auxiliary closing chamber in parallel with the main chamber of the cut-out switch; this auxiliary closing chamber is constituted by an insulative casing which is generally made of ceramics such as porcelain and contains firstly a resistor which has a stationary contact at one of its ends and secondly a movable contact which is actuated by a countershaft mechanism controlled by the switch bar of the contacts of the main cut-out chambers. This mechanism then closes this moving contact a few milliseconds before the main chamber and opens it before the contacts of the main chamber part, since the auxiliary closing chamber is assumed not to have any circuit breaking capability.
Such a device with its rather complex mechanism is not very cheap.
Indeed, to obtain high dielectric strength in the opening position the contacts of the resistor should normally be in the middle of the casing which contains the resistor; this leaves only half the casing for the resistor and leads to inefficient use of the space provided by this casing.
Further, in the majority of cases, one resistor and one pair of contacts are necessary per main chamber, one of the contacts being a stationary contact and the other being a moving contact.
Lastly, in the case where two resistor stages are used successively, i.e. where a first resistor is firstly switched in, then a second resistor with a lower resistance before the main chamber closes, the countershaft mechanism becomes more complex and the extra energy required from the switching unit is greater.
The invention aims to produce a closing device for a high-voltage cut-out switch which uses the insulative casings of the auxiliary chambers more efficiently by reducing their volume, as well as to simplify the production and operation thereof and in the case where there are two stages of resistors, to reduce the number of resistors per phase.